1. Technical Field
Various embodiments of the present disclosure relate to a method of controlling a motor driven power steering system, and more particularly, to a method of controlling a motor driven steering system, when a driver steers a steering wheel to one side (left or right) end of a steering wheel and then, in a state in which all the steering related systems (e.g., machinery, tires, etc.) are twisted to the end, re-steers to the end of the same direction, that can reduce the additional amount of impact generated at the time of re-steering to protect the mechanical system and reduce the impact noise.
2. Related Art
In general, a hydraulic power steering system that forms a hydraulic pressure in a hydraulic pump and assists the assistive steering force, and a motor driven power steering system (hereinafter, referred to as “MDPS”) that assists the assistive steering force using a driving torque of an electric motor have been used as an auxiliary power steering system for reducing the assistive steering force of a driver at the time of steering a vehicle.
Such a motor driven power steering system employs a rack-end-stop logic or soft-end-lock logic which reduce the amount of impact generated when the driver steers to the ends.
However, in the conventional rack-end-stop (soft-end-lock) logic, there is a problem that a steering noise and impact, and a sense of heterogeneity are generated by the tire or the mechanical elasticity characteristics (i.e., the inertia characteristic which tends to return to the state where the steering wheel is twisted to the end at the steering end after the reverse steering after being already twisted to the end) when steering is performed at one end (i.e., the left end or the right end) of the steering angle and then steering to the end or the running direction (i.e., the right end or the left end).
In addition, in the conventional rack-end-stop (soft-end-lock) logic, when an output limit value tuned on the basis of the normal road surface condition is applied to a high friction road surface, there is a problem that a sense of heterogeneity is generated due to the lack of output as the end output is limited, on the other hand, when the output limit value tuned on the basis of the normal road surface condition is applied to a low friction road surface, the output limit value becomes insufficient and the rack-end-stop logic (or an output limit logic) is not operated properly, therefore, an end impact noise and a sense of heterogeneity are generated.
The related art of the present invention is disclosed in Korean Patent Registration No. 10-0247334 registered on Dec. 10, 1999 and entitled “A motor driven power steering system”.